Previous workers have shown that acute myocardial infarction causes cellular electrophysiological abnormalities and potentially fatal arrhythmias. L-alpha-lysophosphatidyl choline, a metabolite found in ischemic tissue, can reproduce ischemic electrophysiological abnormalities in normal cardiac tissues. We propose to use a double microelectrode voltage clamp technique to identify the transmembrane ionic currents induced by lysophosphatidyl choline which cause abnormal automaticity, partial resting membrane depolarization, and post-repolarization refractoriness. By defining the ionic currents responsible for these ischemic cellular electrophysiological abnormalities we will be able to propose rational methods to prevent or reverse these abnormalities. We postulate that modification of the ischemic transmembrane currents will importantly modify the course of potentially fatal ischemic cardiac arrhythmias in man.